We consider the spinless Dirac fermions on a honeycomb lattice, whose
low-energy effective theory in physical \(2+1\)  dimensions can be expressed as
the Lagrangian density[1]}, [2]}, [3]}
\(\mathcal {L}_{\psi }=i\bar{\Psi }\gamma ^{\mu }\partial _{\mu }\Psi ,\) 
